Stationary wave interpolator

ABSTRACT

In a stationary wave interpolator for detecting very rapid movements of objects with high resolution in real-time operation, the mode distance frequency of a laser is fed to a first conductive path and the mode distance frequency plus/minus the Doppler shift is fed to a second conductive path. The two conductive paths are connected by double balanced mixers which are connected in parallel, whose reference inputs are connected to the first conductive path and whose measurement inputs are connected to the second conductive path. The outputs of the double balanced mixers are connected to a digital discriminator for decoupling a phase-shifted Doppler frequency.

BACKGROUND OF THE INVENTION

a) Technical Field

The present invention is directed to a stationary wave interpolator inwhich two conductive paths are connected in each instance with a seriesconnection comprising a photodiode, a hybrid amplifier and a double-holecore, in which the photodiode assigned to the first conductive path isprovided for detecting the mode distance frequency of a laser and thephotodiode assigned to the second conductive path is provided fordetecting the mode distance frequency plus/minus the Doppler shift of aninterferometer, in which the first conductive path is covered by anangle grid having a grid measurement which increases gradually andbeginning with a starting angle and ending with an ending angle, and inwhich all component elements and connections are arranged on a carrieras dielectric material.

The invention is applicable in any measurement technique. It is useablein an advantageous manner particularly where high speeds of objects,e.g. rotational and translational movements at ultra-precisionprocessing machinery, occur at high incremental resolutions.

b) Background Art

All known solutions for carrier frequency methods allow only a lowobject displacement speed, e.g. approximately 50 mm/s at λ/256, becauseof the low carrier frequency of the Zeeman He-Ne laser withapproximately 2 MHz at high interpolation rates. Accordingly,resolutions of λ/1024 at an object displacement speed of 100 mm/s cannotbe realized. Further, increasing the resolution by multiplying thecarrier frequency involves a very high expenditure on circuitry (asdemonstrated in U.S. Pat. No. 3,788,746), wherein no real-timeprocessing is possible in rapid systems. Further, solutions are known inwhich disadvantageous transit time effects (delays) occur with reversalof direction of the object because of a control deviation of the phaseregulating loop caused by hysteresis. Accordingly, it is not possible toincrease the resolution in real-time processing, since an A/D signalconversion time (interpolation) leads to disadvantages (serial dataevaluation).

SUMMARY OF THE INVENTION

The invention has, as a primary object, providing a stationary waveinterpolator which enables a high resolution in real-time operation inrapid systems (parallel signal processing).

This object is met, according to the invention, in a stationary waveinterpolator in that a plurality of double balanced mixers are connectedby their reference input to a first conductive path, in that thereference input of a first double balanced mixer is guided so as to belocalized at the location of the starting angle of the first conductivepath, in that other double balanced mixers are connected to the firstconductive path by their reference inputs so as to be localized at adistance of the increasing grid measurement until the ending angle, inthat the double balanced mixers are connected to the second conductivepath by their measurement input, and in that the outputs of the doublebalanced mixers are connected to a digital discriminator for decouplinga phase-shifted Doppler frequency. This provides the possibility ofparallel evaluation, e.g. via ASIC. The double balanced mixers arepreferably constructed as conventional hybrid networks which allowdifferential frequencies of two input frequencies to be transmitted.

The dielectric material is advantageously a ceramic work material.

In an advantageous further development of the invention, the conductivepaths are constructed as arc-shaped strip lines which are divided intoportions corresponding to the grid. The carrier also preferably has anarc-shaped cross section corresponding to the arc shape of theconductive paths.

The first conductive path should advantageously have a lengthcorresponding to the value λ/2 of the mode distance frequency.

In the invention, at least two double balanced mixers are to be providedwhich are coupled with the first conductive path by their referenceinputs in the grids and correspond to the angles 0° and 90°. However, itis particularly preferred that the coupling be effected in grids whichare equivalent to angles of 5.625° or 11.25°.

A further advantageous construction of the invention also consists inthat the second conductive path is designed as a symmetrical strip linenetwork.

When operating the arrangement according to the invention, thephotodiode assigned to the first conductive path detects a mode distancefrequency f₁ ; f₂ originating from a laser. The photodiode of the secondconductive path detects a mode distance frequency plus/minus the Dopplershift f₁ ; f₂ ±Δf₂ which is fed into the measurement channel from theinterferometer. The amplitudes of the photodiode output signals areincreased in each instance via the hybrid amplifiers connecteddownstream, so that the subsequent double-hole cores are operated insaturation (amplitude stabilization). Stabilization can also be achievedby a diode constant current.

The amplified and thus stabilized signals are fed via the conductivepaths to the double balanced mixers, mixed in the latter and then fed tothe digital discriminator for evaluation in real-time operation asparallel processed signals.

The photodiodes are advantageously constructed as avalanche diodes.

The substantial advantages of the invention consist in that the doublebalanced mixers are exactly assigned to the phase angle of the standingwave formed on the first conductive path so that a high resolution ispossible in real-time operation in fast systems, particularly in laserpath measurement systems. Rapid movements of objects can be detectedusing relatively simple means.

For a better understanding of the present invention, reference is madeto the following description and accompanying drawings while the scopeof the invention will be pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows a basic wiring diagram for a stationary wave interpolatoraccording to the invention; and

FIG. 2 shows the circuit of an advantageous realization of theinvention.

The reference numbers in the drawing have the following meanings:

    ______________________________________                                        1             double balanced mixers                                          3             first conductive path                                           4             carrier                                                         6             second conductive path                                          5, 13         hybrid amplifiers                                               7, 14         double-hole cores                                               8             resistor                                                        9, 15         photodiodes                                                     16, 17        inputs                                                          18, 19, 20, 21                                                                              outputs                                                         22, 23, 24, 25                                                                              reference inputs                                                26, 27, 28, 29                                                                              measurement inputs                                              30 to 58      electrical connections                                          59            phase discriminator                                             ψ.sub.0,1,2 . . . n                                                                     interpolation angles                                            f.sub.1 ; f.sub.2                                                                           mode distance frequency                                         f.sub.1 ; f.sub.2 ±Δ f.sub.2                                                       mode distance frequency plus/minus                                            the Doppler shift                                               A Quad B      signal output for computer                                                    coupling                                                        forward, reverse                                                                            counting chain forward, reverse                                 ______________________________________                                    

PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

The basic connection arrangement of the stationary wave interpolator,according to the invention, according to FIG. 1 comprises a seriesconnection of a photodiode 9, a hybrid amplifier 5 and a double-holecore 7 whose output is connected, via a line 33, with a first conductivepath 3 which is connected to ground potential by its other end via aline 34 and a resistor 8.

Another series connection comprising a photodiode 15, a hybrid amplifier13 and a double-hole core 14 is connected, via a line 58, with a secondconductive path 6. The first conductive path 3 is provided with an anglegrid from ω₀ to ω_(n), wherein the starting angle ω_(o) can be freelyselected and fixed. The grid ends at an ending angle ω_(n) with a gridmeasurement which increases gradually in increments of Δω. The increaseΔω corresponds to the angle or the distance between two adjacent grids,e.g. ω_(o) and ω₁.

The two conductive paths 3, 6 can be constructed in an arc-shaped (i.e.curvature with finite radius, vertical to the drawing plane) or planarmanner (i.e. curvature with infinite radius). Similarly, a carrier 4 ofdielectric material on which all component elements and connections arearranged is provided with an outer surface which is either curved orplanar, so that it has an arc-shaped cross section.

The conductive paths 3, 6 are connected by a plurality of doublebalanced mixers 1 connected in parallel whose reference inputs 22 areconnected with the first conductor path 3, wherein a first doublebalanced mixer 1 is coupled with its input 22 at the starting angleω_(o). Since at least two double balanced mixers 1 are to be provided inorder to realize the invention, the second double balanced mixer 1 is tobe coupled with its reference input 22 at location ω_(n). The doublebalanced mixers 1 further comprise measurement inputs 26 which areconnected with the second conductive path, as well as outputs 18 whichare connected to a digital discriminator 59 comprising a linking ofsixteen comparators and exclusive-OR gates, the signals A Quad B beingavailable at the output of the latter. The A-Quad-B signal output can beprovided as an interface for the computer coupling. Moreover, thedigital discriminator 59 supplies counting chains for theforward-reverse counter or a similar information converter supplying themeasurement value.

Practical construction of the invention is possible with the describedcircuit arrangement according to the principle.

FIG. 2 shows the invention in a particularly advantageous embodimentform. The conductive paths 3, 6 are connected in this instance bysixteen double balanced mixers 1 connected in parallel. In accordancewith this quantity, the grid measurement on the conductive path 3 has anamount Δω=11.25° at ω_(o) =0° and ω₁₆ =169.75°. The conductive path 3 isconstructed as a strip line having a length corresponding to the valueλ/2 of the mode distance frequency f₁ ; f₂ of the laser. The secondconductive path 6 is designed as a symmetrical strip line network whichconnects the measurement inputs 26, 27, 28, 29 of the shown doublebalanced mixers 1 as well as the other measurement inputs of the doublebalanced mixers 1 which are not shown in FIG. 2.

In operating the arrangement a mode distance frequency f₁, f₂originating from the laser is detected by the photodiode 9 which isconstructed in the shown example as an avalanche diode, while thephotodiode 15, likewise an avalanche diode, receives the mode distancefrequency plus/minus the Doppler shift f₁ ; f₂ ±Δ f₂ coming from aninterferometer in the measurement channel. The diode bias voltages areselected in such a way that the two photodiodes 9, 15 work in themaximum range. The hybrid amplifiers 5, 13 connected downstream increasethe signal amplitude so that the following double-hole cores 7, 14 areoperated in saturation (amplitude regulation). Accordingly, it ispossible that the laser drift capacity can fluctuate by at least anorder of magnitude and that the plane mirror in the measurement systemupstream can be tilted more sharply compared with conventional laserpath measurement systems.

The amplified and regulated signals f₁ ; f₂ and f₁ ; f₂ ±Δ f₂ are fed tothe double balanced mixers 1 via the conductive paths 3, 6, wherein thesignal f₁ ; f₂, corresponding to the grid in each instance, is connectedto the reference inputs 22, 23, 24, 25 of the shown double balancedmixers 1 and the other reference inputs of the double balanced mixers 1which are not shown, and the signal f₁ ; f₂ ±Δ f₂ reaches themeasurement inputs of the double balanced mixers 1 via the conductivepath 6. The signals are mixed in the double balanced mixers 1.

Sixteen signals from Δ f₂ +ω₀ to Δ f₂ +ω₁₆ are tapped at the outputs 18,19, 20, 21 of the shown double balanced mixers 1 and at the otheroutputs of the double balanced mixers, not shown in FIG. 2, in parallelwith the corresponding phase shifts in real-time operation as a functionof the displacement of the object to be measured (measurement mirror,not shown in the drawing) and are fed to the digital discriminator 59for evaluation. The sign of the Doppler frequency ±Δf₂ is determined andcounting chains which are correct with respect to the sign are prepared.

The double balanced mixers 1 supply an alternating signal without a d.c.component, which signal is triggered in the zero point of the amplitude.Amplitude disturbances, e.g. brought about by maladjustment of anoptical system connected prior to the stationary wave interpolator or bytilting of the measurement mirror in this system, do not have adisruptive effect. In super-rapid and high-resolution systems, theamplitude is regulated via a second gate of the dual-gate transistors ofthe hybrid amplifiers 5, 13. Evaluation circuits which correct the zeropoint are to be used if necessary during fluctuations of the zero pointof the double balanced mixer 1 during fast movements of the measurementmirror. The mixer output frequency of zero Hertz is allowed when theobject to be measured is stationary. A correction of nonlinear transittime errors is possible by dividing the Doppler frequency ±Δ f₂ intointervals and varying the divisor factor in each interval.

While the foregoing description and drawings represent the preferredembodiments of the present invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the true spirit and scope of the presentinvention.

What is claimed is:
 1. A stationary wave interpolator comprising: twoconductive paths each connected with a series connection including aphotodiode, a hybrid amplifier, and a double-hole core; said photodiodeassigned to the first conductive path being provided for detecting themode distance frequency of a laser and said photodiode assigned to thesecond conductive path being provided for detecting the mode distancefrequency plus/minus the Doppler shift of an interferometer, said firstconductive path being covered by an angle grid which starts at astarting angle (ω₀) and ends with a gradually increasing gridmeasurement at an ending angle (ω_(n)); all component elements andconnections of said interpolator being arranged on a carrier ofdielectric material; a plurality of double balanced mixers, havingreference time inputs and reference inputs, being connected to the firstconductive path by their reference time input; the reference input of afirst double balanced mixer being guided so as to be localized at thelocation of the starting angle (ω₀) of the first conductive path; saidother double balanced mixers being connected to the first conductivepath by their reference inputs at a distance of the increasing gridmeasurement up to an ending angle (ω_(n)); said double balanced mixersbeing connected to the second conductive path by their measurementinput; and said outputs of the double balanced mixers being connected toa digital discriminator for decoupling a phase-shifted Dopplerfrequency.
 2. Stationary wave interpolator according to claim 1, whereina ceramic work material is used as dielectric material.
 3. Stationarywave interpolator according to claim 1, wherein the conductive paths areconstructed as arc-shaped strip lines.
 4. Stationary wave interpolatoraccording to claim 3, wherein the carrier has an arc-shaped crosssection.
 5. Stationary wave interpolator according to claim 1, whereinthe first conductive path is provided with a length corresponding to thevalue λ/2 of the mode distance frequency.
 6. Stationary waveinterpolator according to claim 1, wherein the photodiodes areconstructed as avalanche diodes.
 7. Stationary wave interpolatoraccording to claim 1, wherein the second conductive path is designed asa symmetrical strip line network.
 8. Stationary wave interpolatoraccording to claim 1, wherein the double balanced mixers comprisemeasured hybrid modules.